1. Technical Field
The present disclosure relates to power supplies, and more particularly to a power supply control circuit and a power supply control method using a standby control circuit to cut off power to a microprocessor.
2. Description of Related Art
Referring to FIG. 1, one example of a power supply control circuit 1 is employed in an electronic product (not shown) including a load circuit (not shown), to enable and disable the load circuit. The power supply control circuit 1 includes a first input port 2, a second input port 3, a relay 4, a first power supply circuit 5, a second power supply circuit 6, a microprocessor 7, and a switch 8. The relay includes a control member and a switch member. The second power supply circuit 6 includes a transformer 9 and a rectify-and-filter circuit 10.
The first power supply circuit 5 is coupled to the first input port 2 and the load circuit, as well as the second input port 3 through the switch member of the relay 4. The transformer 9 includes a primary coil having two ends coupled to the first and second input ports 2, 3, respectively, and a secondary coil coupled to the microprocessor 7 through the rectify-and-filter circuit 10. The microprocessor 7 is coupled to the control member of the relay 4 and the switch 8.
The first and second input ports 2, 3 are coupled to an external power source (not shown). The second power supply circuit 6 receives an alternating current (AC) voltage signal from the power source through the first and second input port 2, 3, converts the AC voltage signal to a first direct current (DC) voltage signal through the transformer 9 and the rectify-and-filter circuit 10, and outputs the first DC voltage signal to the microprocessor 7 so as to output a power thereto.
After the microprocessor 7 is powered on, pressing of the switch 8 to switch on the same generates a pulse signal. The microprocessor 7 receives the pulse signal and controls the control member of the relay 4 to turn on the switch member of the relay 4 in response to the pulse signal. Thereafter, the first power supply circuit 5 receives the AC voltage signal from the power source through the first and second input ports 2, 3, converts the AC voltage signal to a second DC voltage signal, and outputs the second DC voltage signal to the load circuit so as to output a power thereto.
After the first power supply circuit 5 is activated, a subsequent pressing of the switch 8 generates a second pulse signal. The microprocessor 7 receives the second pulse signal and controls the control member of the relay 4 to turn off the switch member of the relay 4 in response to the second pulse signal. Thereafter, the first power supply circuit 5 is cut off from receiving the AC voltage signal from the power source and stops conversion of the AC voltage into the second DC voltage signal so as to cut off the power thereto.
One disadvantage of the power supply control circuit 1 is that the second power supply circuit 6 continuously outputs the first DC voltage signal to the microprocessor 7 when the first power supply circuit 5 is activated or deactivated. Therefore, the transformer 9 of the second power supply circuit 6 is still at work when the first power supply circuit 5 is deactivated to cut off the power to the load circuit, which results in a power waste.